Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $224.66   10.290%   $247.7775   $247.78   $247.80   $247.80  
  Purchase #2 $81.96   13.161%   $92.7468   $92.75   $92.75   $92.70  
  Purchase #3 $243.50   5.458%   $256.7902   $256.79   $256.80   $256.80  
  Purchase #4 $21.99   7.542%   $23.6485   $23.65   $23.65   $23.60  
  Purchase #5 $84.49   8.779%   $91.9074   $91.91   $91.90   $91.90  
  Purchase #6 $178.48   8.112%   $192.9583   $192.96   $192.95   $193.00  
  Purchase #7 $53.97   9.712%   $59.2116   $59.21   $59.20   $59.20  
  7 purchase totals = $889.05       $965.0403   $965.05   $965.05   $965.00